Feature: Add token based registration creation and management

[Sleuth56]

As of Synapse version 1.42.0 users can now register with tokens generated by server admins. This is a great new feature as it allows server admins to easily have a private server while still making it easy to add new users. This will greatly increase the security of the matrix ecosystem as well as help prevent future spam attacks.

Matrix spec: https://github.com/govynnus/matrix-doc/blob/token-registration/proposals/3231-token-authenticated-registration.md
Synapse implementation: matrix-org/synapse#10142
Synapse admin docs: https://matrix-org.github.io/synapse/latest/usage/administration/admin_api/registration_tokens.html
Synadm implementation: JOJ0/synadm#42